1. Field of the Invention
The present invention relates generally to augers and more particularly to a device for connecting a centerless auger to a rotatable member.
2. Description of the Related Art
Image forming devices such as printers, copiers, facsimile machines, and the like, produce unusable “waste” or residual toner as a byproduct of an electrophotography (EP) process. Ideally, all of the toner that is picked up by a photoconductive drum such as from a developer roll in the case of a single component development process or a magnetic roll in the case of a dual component development process would be transferred onto a media sheet (or an intermediate transfer member (ITM) in the case of a two-step toner transfer process). However, due to inefficiencies within the image transfer process, all of the toner put on the photoconductive drum does not get transferred to the media sheet or ITM. This residual toner left on the photoconductive drum after it has contacted the media sheet or ITM must be removed before the next image is formed to avoid contamination by the residual toner. For this purpose, a cleaner blade or a cleaner brush is placed in contact with the photoconductive drum to wipe the residual toner from its surface. The residual toner removed by the cleaner blade or cleaner brush is then stored in a sealed residual toner compartment disposed adjacent the photoconductive drum to prevent it from being distributed inside the printer. The residual toner compartment should preferably be sized to hold a large amount of residual toner to minimize frequent removal from the image forming device. It is also desirable for the overall size of the image forming device to be as small as possible, limiting the size of the residual toner compartment. Accordingly, there is a need for a mechanism to maximize the amount of residual toner that can be stored within the residual toner compartment.
Augers have proved to be an effective means of moving toner from one area to another for a wide variety of toner applications. Augers used for transferring residual toner are usually made from either molded plastic or metal wire stock. However, each of these types of augers has its own drawbacks. For example, injection molded plastic augers have proved to be easier to manufacture than the metal wire variety. In addition, providing a drive for a plastic auger is more straightforward because the drive shaft for the auger can be molded in the same cavity as the helix, resulting in a simple one piece design. However, the problem with the plastic molded augers is that these are most often resistant to bending and can only transfer waste toner in straight channels. Comparatively, the metal wire augers have an advantage of being able to bend and as a result transfer the residual toner through a curved channel effectively. Additionally, the space in the center of a centerless auger also carries material thereby permitting a higher transfer rate.
A barrier for practical implementation of metal wire augers is the need for a metal drive shaft used to connect the auger with its drive source. Having a metal drive shaft on which to fix the auger is advantageous in that the auger can be soldered or welded onto the drive shaft without an attachment part such as a screw, pin or other retainer. However, metal drive shafts add significant cost to the overall auger design, decreasing its likelihood for use in mass production.
Some manufacturers have used a plastic drive shaft instead of a metal drive shaft to reduce some of the above problems faced by the metal drive shafts. For example, the cost of the drive component is reduced substantially by using plastic instead of a machined or cast metal part. Also, an additional processing station such as welding or soldering is not needed if the drive is made from plastic. Finally, a plastic drive shaft makes it easier to attach the gearing that is needed to turn the assembly.
However, securing or coupling the metal auger to the plastic drive shaft is a significant obstacle in designing a plastic drive shaft. The coupling mechanism must fit inside the auger channel without interference in order for the auger to turn freely. Further, the size of the coupling mechanism is also generally very small, making it difficult to transmit the torque needed without risk of breakage. An alternative employment of a coupling mechanism between the auger and the plastic drive shaft is to mold the auger into the plastic drive shaft to form a unitary device. Unfortunately, this method is very sensitive to manufacturing parameters and is a much more expensive alternative to hand assembly. For example, it is difficult to clamp onto the auger with an injection molding machine without damaging the auger and without allowing molten plastic to leak out along the auger wire. Further, the metal auger may not adhere sufficiently to the plastic drive shaft and can be easily disconnected from the plastic drive shaft by unscrewing the auger from the plastic drive shaft.
Thus, there is a need to provide a secure coupling between an auger and corresponding drive shaft that addresses at least some of the above problems and still provides a reliable residual toner removal operation within the residual toner compartment.